Angiogenesis is a promising new therapeutic modality for the treatment of coronary artery disease (CAD). However, despite impressive results of animal studies from our laboratory as well as others, preliminary clinical use of angiogenic therapy in humans has only resulted in modest if any objective benefit. Patients with end-stage CAD, who represent the population currently targeted by angiogenic therapy, virtually all have advanced endothelial dysfunction that results in abnormal production and response to endothelial substances. Since angiogenic growth factors operate in large part through the release of endothelial-derived nitric oxide via the activation of tyrosine kinase receptors, the observed failure of effect in patients with end-stage CAD may relate to a deficiency in the stimulated release of these endothelial-derived substances. This research proposes to define the role of endothelial function on the effects of exogenous growth factor therapy and on the endogenous angiogenic response to myocardial ischemia. To this end, a hypercholesterolemic porcine model will be used that recreates myocardial microcirculatory changes similar to those encountered in humans with CAD. Several study groups that include animals with normal, dysfunctional, or pharmacologically- treated endothelium will be created, in which surgical induction of chronic myocardial ischemia and implantation of sustained- release growth factor devices (FGF-2, VEGF, or placebo) will be performed. In each study group, endothelial responses will be assessed in vitro on microvascular reactivity studies, and the angiogenic response will be quantitatively determined at the functional, microvascular, histological, and molecular levels, using tools such as isotope-labeled microsphere assays of myocardial perfusion, sonomicrometry, immunocytochemistry and real time PCR analysis. By clarifying the role of the endothelium and endothelial-modulating agents in the functional angiogenic response, the findings from this research will lead to a more complete understanding of therapeutic angiogenesis, and may allow for the development of this modality towards a safe, effective, and attractive option for the treatment of CAD.